Concentration control



Feb. 21, 1950 F. w. SCHMITZ CONCENTRATION CONTROL Filed Dec. 26, 1945Fwd MSM 3M .THM

Patented Feb. 21, '1950 CGNCENTRATION CONTROL Frederick W. Schmitz,Irvington, N. J., assignor to Research Corporation, New York, N. Y., acorporation of New York Application December 26, 1945, Serial No.637,280

4 Claims.

This invention relates to air conditioning systems, and control meanstherefor, and to a method for conditioning air. It is particularlyconcerned with air conditioning systems in which air or other gas to beconditioned is contacted with an extended surface of a hygroscopicsolution, prefrably maintained at a predetermined temperature andpreferably comprising an aqueous solution of triethylene glycol, calciumchloride or the like. In the removal of moisture from the air, thehydroscopic solution -becomes diluted and must be concentrated forre-use. To effect concentration, the vdilute solution, or a part of it,is passed to a concentrator. The concentrated solution is thenpreferably cooled and thereafter re-used to dehumidify additional gas.

` A principal object of the invention is to provide asystem of thecharacter described including improved control means to sense changes inthe concentration of the hygroscopic solution and to regulate theoperation of the concentrator in accordance with such changes.

A further object is to provide a relatively simple and highly reliabledevice for sensing changes in concentration or measuring theconcentration of solutions whose boiling point varies withconcentration.

Another object is to provide a process for conditioning air or other gasinvolving a unique and simple step for effectively controllingconcentration of the hygroscopic solution employed.

' An illustrative embodiment of the principles of the invention will bemore particularly described with reference to the accompanying drawingin which:

Fig-1 is a diagrammatic representation of an air conditioning systemincluding a control device embodying lthe principles of the invention,and

Fig. 2 is a sectional elevation of a representative embodiment of thecontrol device of the invention.

In the drawing, the air conditioning system shown includes a dehumidierI, a hydroscopic solution heater 2, a concentrator 3 and a control.device 4. The interrelationship of these components, their separateconstruction and their respective functions will be more fully describedhereinafter.

The dehumidifier I typically takes the form of a housingproviding anenclosed chamberl having an air inlet 5, a transverse baille 6 directingthe stream of air downwardly over a coil l, uplwardly through sprayeliminators 8 and through Youtlet 9` to the space to be conditioned. Asuit- 2 able blower or fan I0 is provided for drawing air through thedehumidifle I Over the outside of coil 1, a lm of hygroscopic solution,such as an aqueous solution of v.triethylene glycol, is caused to ow andinside the coll a cooling medium, such as water, is circulated at apredetermined temperature. Hygroscopic solution is sprayed upon the topof the coil from spray heads I I; it flows by gravity down the coil,drops to the bottom of the dehumidifier and is collected in sump I2.Cooling medium is introduced to the coil through conduit I3 and is ledaway from the coil through another conduit I4.

The hygroscopic solution which collects inthe sump I2 is picked up by apump I5 anddelivered to the line I6 from `which it is in partrecirculated to the spray heads I I through pipe I1 and in part passedto the concentrator through pipe III.

Valves are provided in pipes II and I8 for regulating the amounts ofsolution to be recirculated and passed to the concentrator.

The concentrator 3 has avcasing I9 providing a Vertical shaft and havingan air inlet 20 near the bottom and an air outlet. 2I at the top. Ablower or fan 22 sucks air through the shaft from bottom to top.

Inside the shaft there are located three indirect heat exchangers,typically, finned coils. The uppermost, 23, of these is connectedbetween the pipe I8 and the solution heater 2 so that hygroscopicsolution from the dehumidifier sump I2 flows inside the coil on its Wayto the heater. Coil 23 functions as a condenser for recovering a portionof the triethylene glycol from the air leaving the concentrator andlreturning such portion to the concentrator; it further functions as apreheater for the solution going to the heater 2.

The intermediate coil 24 is a steam coil, inside of which steam iscirculated from a source (not shown). Steam is led to the coil in pipe25 and condensate is conducted away'from the coil in pipe 26. A controlvalve 21 regulates the admission of steamto the coil; such valve may beof the on-oli or modulating type; it, in turn', is

regulated by the control device 4 in a manner to be more fully explainedhereinafter. A spray of hygroscopic solution from spray heads 28 flowsover the outside of coil 24 and is heated thereby to the desiredconcentrating temperature.

The lower` coil 29I is positioned below the air inlet 20 in the sump ofthe concentrator. Cooling water from the dehumidifier is circulatedinside the coil, the-function of which is to cool hot concentratedhygroscopic solutiminy the sump to a temperature approximately equal tothe temperature of the dehumidifier.

Between the air inlet and the steam coil 24 is positioned a column ofpacking 30. The packing may consist of Raschig rings or other extendedsurface material over which hot hygroscopic solution owscounter-currently to the stream of air rising in the concentrator.

Concentration of the hygroscopic solution takes place principally in theregion of the steam coil 24 and packing 30, although some may occur inthe spray region above the steam coil. In concentrating aqueoussolutions of triethylene glycol, some glycol is carried above the sprayregion as entrained and vaporized glycol. The condenser coil 23 coolsthe gas leaving the concentrator and condenses and returns to theconcentrator much of the glycol which would otherwise be lost to thesystem.

On its way to the concentrator from the dehumidifier, the hygroscopiosolution to be concentrated, after leaving the condenser coil 23, passesby Way of pipe 3| to the solution heater 2 Where it is circulated inindirect heat exchange relationship with steam and thereby heated nearlyto the concentrating temperature. It is then conducted to the sprayheads 28 through pipe 32. Steam is led to the heater by pipe 33 andcondensate is removed by pipe 34. Concentrated hygroscopic solution owsfrom the concentrator back to the sump of the dehumidier through returnduct 35.

In operation, where air is to be conditioned by dehumidiiicationv `andcooling, its sensible and latent heat are transferred to the hygroscopicsolution flowing over the outside of the coil 1 in the dehumidifier Iand thence, by indirect heat exchange, to the cooling water circulatingthrough the coil. Moisture is removed from the air by the hygroscopicsolution causing dilution of the latter.

If conditioned air of substantially uniform character is to be deliveredby the apparatus, the concentration of the hygroscopic solution must bemaintained at a substantially constant value. In the apparatus shown,this condition Ais achieved by controlling the operation of theconcentrator 3 in accordance with the concentration of the solutionbeing fed to the spray heads II. It will be understood, however, thatsuch control may, if desired, be in accordance either with theconcentration of the solution dripping from the bottom of the coil 'I orwith that of the solution found in the sump of the dehumidifier.Suitable sampling devices may be employed, in the latter 5f cases, forremoving control samples from the bottom of the coil 1 or from the sumpI2 of the dehumidier. The control device 4 has an outer casing 36, whichis preferably cylindrical in crosssection, and an inner concentriccylindrical casing 31. The space between the outer and inner casingsprovides a reservoir for a control sarnple of hygroscopic solution whichis bled into the reservoir from the main solution 'line I6 through pipe38. Pipe 38 is equipped with a valve 39 and a metering orice 4t limitingthe flow of solution to the` reservoir to a preselected value. Thereservoir is providedv with an overflow pipe 4I which maintains theliquid level in the reservoir constant and returns excess solution tothe sump I2 of 'the dehumidifier. Such excess solution may be returnedto the system at any other convenient point, for example, it may be led`to the concentrator and there mixed with the solution in the sump' of'the concentrator.

A heater element 42 is positioned in the lower part of the inner casing31. Preferably this heater element is of the electric resistance type. Atemperature-sensitive device 43 is located in the upper part of theinner casing and is op eratively connected by suitable means 44 to thevalve 21 controlling the admission of steam to the concentrator. y

A port 45 admits solution from the reservoir to the bottom of the innercasing 31 and discharge ports 46, located near the top of the innercasing, provide for overilow of solution from the central chamber.Suitable insulation 41 surrounds the lower portion of the inner casingfor minimizing the transfer of heat from the inner or boiling chamber tothe solution sample reservoir.

The capacity of the heater element 42 is so selected that active boilingof the solution in the central chamber can be quickly established andcontinuously maintained without, however, causing undue heating of thesolution in the reservoir. When active boiling has been established; thecentral chamber acts as a vapor lift continuously circulating anequilibrium mixture of boiling solution and Vapor into contact with thetemperature-sensitive element 43. Some of the mixture is dischargedthrough ports 46 while additional solution is added to the boilingchamber through the lower port 45.

It will be seen that the element 43 at all times senses the true boilingpoint of a control sample of solution continuously being drawn from thebody of solution being pumped to the spray heads of the dehumidier. Asthe solution becomes cli-I luted through absorption of moisture fromfgasbeing treated, its boiling point decreases to a temperature at which thetemperature-sensitive element has been set to turn on or increase theflow of steam through the valve 21. Conversely, as the solution becomesconcentrated through action of the concentrator 3, its boiling pointrises to a higher temperature at which the temperature-sensitive elementhas been adjusted to turn 01T or decrease the flow of steam to theconcentrator. 'I

In this manner, the limits of control can be selected in practice tomaintain the concentration of the solution within narrow bounds.Illustrative of the degree of control which can be achieved, an aqueoussolution of triethylene glycol which is in equilibrium with the partialpres? sure of water vapor in air at about 0% relative humidity at '70 F.has the relatively great varia tion in boiling point of 3 F. for therelatively small variation in concentration of about 0.5%.. Similarly,an aqueous solution of triethylene glycol in equilibrium with air atabout 25% relative humidity at 70 F. exhibits a variation in boilingpoint of 2 F. for a variation in concentration of approximately 1.0%.Thus, it is apparent that small changes in concentration of hygroscoplcsolution are reflected in relatively large changes in boiling point sothat control of concentration in accordance with boiling point resultsin very satisfactory operation.`

Alternatively to its control of the heat supply to the steam coil 24, ortogether therewith,'the control device 4 may be arranged to' regulatethe heat supply to the solution heater 2','which 'for present purposes,may be considered tobe a part of the concentrator. It may also turn oil?anden', or modulate the fan 22 drawing air through ,the concentrator,and may be considered yto control the heat supply and other conditionsin other d types of concentrators, such as vacuum or atmosphericevaporators.

The circuit lill from the temperature-sensitive element may includemeans for actuating an alarm signal if the temperature falls below aselected point. Preferably, however, an auxiliary element may be placedin the path of the overiiow from the boiling chamber which will serve toactuate a signal indicating boil or no-boil.

It will be evident that the control device can be utilized for themeasurement of actual boiling temperatures by connecting to the circuit44 a suitably calibrated instrument.

In many cases the operation of the dehumidifier of a gas conditioningsystem at superatmospheric pressure presents many advantages. Forexample, if air is dehumidined by contact with a hygroscopic solution ata gauge pressure of pounds per square inch and subsequently releasedinto the conditioned space at atmospheric pressure, the hygroscopicsolution may be maintained at a substantially lower concentration, thuseliminating a large amount of corrosion and decomposition difculties.Since the expansion of the air results in a drop in its dry bulbtemperature, it is possible in such a system to maintain comfortconditions with cooling medium of higher temperature than wouldotherwise be effective.

The control device and method of the invention are particularlyadvantageous with such superatmospheric dehumidifying systems. Thehygroscopic liquid in the boiling chamber of the concentrating sensingdevice may be maintained under the same pressure as that of thedehumidifier or the pressure in the sensing device may be atmospheric.In either case, the control element is, of course, set to maintain thehygroscopic solution at a concentration range effective to condition thegas in the dehumidifier to the desired preselected humidity. Forexample, if the gas in the dehumidiiier is maintained under 15 poundsper square inch gauge pressure, the gas will be in equilibrium at 70 F.and a relative humidity of 30% with a triethylene glycol solution of77.3% concentration. A solution of such concentration has a boilingpoint of 230 F. at atmospheric pressure. To provide the same conditionsat atmospheric pressure in the dehumidier, the triethylene glycolsolution must have a concentration of 91.2% and a boiling point of 256F. at atmospheric pressure.

I claim:

1. A device for sensing changes in the boiling point of solutions whichcomprises means providing a generally vertically extending vapor-liftchamber having solution inlet means near its bottom and discharge meansnear its top, means for feeding solution to said chamber means throughsaid inlet means at a pressure less than the solution head equivalent tothe vertical drop between said discharge means and said inlet means,heating means for boiling solution contained in said chamber means, anda temperature-sensitive element mounted in said chamber means in contactwith the actively boiling solution.

2. A device for sensing changes in the boiling point of solutions whichcomprises an outer casing, a substantially vertically extending casingwithin said outer casing providing a vapor-lift chamber and cooperatingwith said outer casing to provide a solution reservoir, said innercasing having a solution inlet port near its lower end and a dischargeport near its upper end, both of said ports communicating with saidreservoir, means for admitting solution to said reservoir, means formaintaining the solution level in said reservoir at a point between saidports, heating means for boiling solution contained in said innercasing, and a temperature-sensitive element mounted in said inner casingin contact with the actively boiling solution.

3. A device for sensing changes in the boiling point of solutions asdefined in claim 2 wherein said means for admitting solution to saidreservoir includes means limiting the rate of admission to a maximumvalue.

4. A device for sensing changes in the boiling point of solutions asdened in claim 2 wherein means is provided for at least partiallyinsulating said reservoir against passage of heat from said vapor-liftchamber.

FREDERICK W. SCHMITZ.

REFERENCES CITED The .following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 173,128 Malligand Feb. 8, 1876507,633 Peck Oct. 3l, 1893 1,747,742 Stein Feb. 18, 1930 2,017,368Magner Oct. l5, 1935 2,094,342 Bichowsky Sept. 28, 1937 2,199,967Bichowsky May 7, 1940

